The invention disclosed and claimed herein generally pertains to a cover or housing for a data acquisition system (DAS) of a computed tomography (CT) imaging system, wherein the housing is configured to allow heat to be readily transferred away from the DAS. More particularly, the invention pertains to a housing of such type which enhances or facilitates air flow, in order to carry heat away from the DAS and thereby significantly reduce image artifacts.
In a CT imaging system or scanner, a gantry rotates an X-ray tube around a patient or other object of scanning. X-radiation projected by the tube, which is not absorbed by intervening patient body structure, is sensed by respective detectors of a detector array. In certain classes of CT products, such as those manufactured by the General Electric Company, the assignee herein, the array comprises solid state detectors which generate electric signals corresponding to the sensed radiation. The signals are coupled to a data acquisition system or DAS, and data acquired thereby is in turn coupled to an image processor, which reconstructs an image of the body structure or other object of interest.
It is intended that images generated by a CT scanner, both of anatomy and of phantoms, be free and clear of any artifacts. Some of the most commonly seen artifacts are rings and bands. These artifacts are not desirable, as they can lead to misdiagnosis by a radiologist. Artifacts can occur due to the malfunction of any one of the sub-systems in the image chain, such as the X-ray tube, detector, DAS or image processing software. However, in the CT product classes referred to above, recently acquired field data has demonstrated that the proportion of artifacts which are specifically caused by malfunction of the DAS may exceed 25 percent. Moreover, it has been suspected that a significant number of other artifacts, for which the cause is not definitely known, may in fact be due to defects in the DAS.
In the above CT product classes, the DAS typically comprises a large number of printed circuit boards, which are electrically coupled together. Those of skill in the art have recognized that a DAS of this type is extremely sensitive. In particular, it has been commonly believed that DAS operation is likely to be disturbed by sudden changes in temperature. Accordingly, current standard practice is to place the DAS within a substantially air-tight enclosure, to enhance temperature stability. In some arrangements, each DAS board is also sealed individually, within its own air-tight compartment. However, notwithstanding such measures, DAS malfunctions continue to cause a significant portion of CT system artifacts, as indicated by the percentage figures set forth above.
In making the invention, it was determined that sealing a DAS of the above type in a substantially air-tight enclosure, as taught by the prior art, had significant drawbacks. More particularly, it was recognized that, while the amount of heat generated by the DAS circuit boards is comparatively negligible, such enclosures tended to retain the heat in close proximity to the DAS. Moreover, the DAS boards continuously receive electric power, and therefore are always generating heat. This results from the conventional practice of keeping a CT system powered up at all times, even when the system is idle, i.e., is not being operated to perform scanning operations.
Through extensive investigation and analysis, the inventor has now determined that under certain circumstances, and during idle periods which are prolonged, the heat retained in a DAS can become significant. Moreover, such heat can degrade DAS performance and be a principal cause of artifacts. More specifically, it has been found that if a CT system is idle for a substantial period, such as at night or over a weekend, and if the system is not well ventilated, the temperature within a conventional DAS enclosure may exceed 60.degree. C. At the same time, the temperature within the surrounding gantry enclosure may be on the order of 30.degree.-35.degree. C. This differential can create certain problems which are considered to have been overlooked, prior to the inventor's recognition thereof. Specifically, when the CT system is placed into operation, the DAS will rotate with the gantry. Initially, rotation will cause the cooler air of the gantry enclosure to draw heat away from the DAS, and the temperature thereof steadily drops. Eventually, DAS temperature will stabilize at the gantry enclosure temperature. However, calibration of the CT system, which must be performed at the beginning of a scan operation, may take place before DAS temperature stabilizes. Because of the extreme sensitivity of the DAS to temperature change, as noted above, the calibration may not be valid when the DAS stabilizes. It is believed that in the past, this situation has resulted in significant artifacts, while the cause thereof was not understood.